Programmable controllers (PCs) are widely used for the control, etc. of a machine tool. The programmable controller (PC) includes a programmable machine controller (PMC) incorporated in a numerical control apparatus and a programmable controller arranged independently of the numerical control apparatus.
Both of these PCs are interposed between the machine tool and the numerical control apparatus, to enable many I/O signals to be transferred therebetween, but the arrangement of these I/O output signals in the numerical control apparatus is different from that at the entrance of the PC. More specifically, the numerical control apparatus has a predetermined standard arrangement of I/O signals by which it adjusts itself to many kinds of machine tools, but each machine tool does not always use all of the I/O signals of the numerical control apparatus and thus has a different arrangement of the I/O signals. Accordingly, when a sequence program of the PC is created, the arrangement of these signals must be changed.
Nevertheless, when the number of the I/O signals is increased, a sequence program having a considerable number of steps must be created to change the arrangement of these signals, which imposes a burden upon the creation of the program. Further, when a detailed specification of a machine tool is changed, the sequence program must be changed, which makes the sequence program incompatible and causes maintenance problems.